The present invention relates to a control system for a hydraulic automatic clutch.
In the case of a vehicle having a hydraulic automatic clutch, the engagement of the clutch is controlled by a fluid pressure supplied thereto. During idling operation of an engine when the vehicle is at a standstill, the fluid pressure supplied to the clutch is kept low enough to assure disengagement of the clutch. For starting the vehicle, the fluid pressure supplied to the clutch is increased in accordance with an input revolution speed, for example, an engine revolution speed, to the clutch in order to engage the clutch. This control concept of the automatic clutch has the following problem. Although the fluid pressure supplied to the clutch during idling of the engine when the vehicle is at a standstill must be suffciently low to assure disengagement of the clutch, if the fluid pressure supplied to the clutch is set excessively low as compared to a certain value at which the clutch begins to engage, it takes a time and allows the engine to race before the clutch starts engaging. If, on the other hand, the fluid pressure supplied to the clutch is adjusted to a slightly low value as compared to the certain value, the fluid pressure supplied to the clutch will exceed the certain value when the idle speed of the engine increases as a result of the use of a choke or the use of a compressor of an air conditioner or the irregular operation of the engine, resulting in an unintentional starting of the vehicle. To avoid such problem, it has been the common practice to set the fluid pressure supplied to the clutch during idling of the engine when the vehicle is at a standstill sufficiently lower than the value at which the clutch engagement initiates. As a result, it has been recognized as an unavoidable operational characteristic of the hydraulic automatic clutch that the engine tends to race prior to clutch engagement and there take place substantial shocks upon clutch engagement for starting the vehicle.